Ok, I've been storing my boats correctly (upright against the wall with the flat part of the hull against the wall), not going ape$hit when tightening straps (and even usually put the boat on the rack hull up), and haven't worn the plastic thin.

Why would I be repeatedly getting warping under the seat?

This is the third boat in a row that this has happened to me. I've only had my most recent victim for maybe a month. It doesn't seem to be affecting the boat while paddling, but it certainly wasn't designed to be there.

The problem is, the hull is dented outward, so putting more material under the seat only gives more to push the dent farther out with. Guess I coulda mentioned that it was bulging out, not cavitated.

As well, the bulges are firm, not floppy as a reference to oil canning would suggest. Makes sense because it wasn't caused by the plastic being worn thin. Maybe I'm misunderstanding why to foam under the seat.

In all three boats, the warpage happens directly below the seat. First was a Dagger, then a WS, now a Pyranha.

Often if you get the bottom of the boat really warm the oil cans will naturally come out. Leaving the boat upside in the hot sun is one way to do this.
I've had some success using a heat gun and gently heating, and then setting bricks or other weights on the affected area.
Definitely worth spending some time with because an oil-can is a prime area for cracks to form.
I'm pretty adamant about never ever tying my boat right-side up. I try not to let other people talk me into tying my boat this way on their car.

I don't know that the way you tie your boat matters very much - especially for a local trip. The only times I've made a point of making sure my boat hull was not in a compromising position was when I drove to Canada or for long trips to Nor. Cal or So. Cal. In about 15 years and probably as many boats, I've never had an oil canning problem.

The thing I've always heard though, is that the way you store your boat is most important. Don't ever store it sitting on its bottom, standing on end or sitting on its side is supposed to be best.

So, Grinch, yours is bulging out? I've never heard of that. On multiple boats too? Damn, you're definitely doing something wrong. The only thing I can think of is that maybe you're dragging over rocks too much going down the river, that's making the hull weaker, and your weight on the seat is pushing the hull out.

I'll keep thinking about it and post here or let you know if I come up with anything

That's not cool, especially if it's the boat we recently exchanged. One reason I originally bought it was that it was more rigid than my previous Jackson playboat.

Is it possible that you adjusted the seat position and forgot to fully tighten up the brackets in the cockpit rim where the seat is hung? I think they're supposed to take the weight so the seat doesn't bear directly on the bottom of the hull. They're awkward to reach in most boats and sometimes loosen up after a bunch of roll practice or playboating.

Fiddleyak, I've read about using the sun to get better heat soak than a heat gun can provide, and will probably try that. What about during winter (heat gun, I know, but it is hard to warm a large area evenly with them).

Dan, I haven't been doing much ELF paddling, but I do enjoy rock splats, spins, splat wheels, and the like. However, the outward bump is firm, not flexible. I don't know, but you might be on to something.

Yeah, Nick, the latest display of this is your old boat, which of course wasn't old at all. Yes, I moved the seat, but everything has been tightened and re-tightened a while back. A quick check just now confirms.

Could it simply be my fit and posture in the boat, the pressures placed at certain points with the large flat surface under the seat most easily warped? In the Pyranha there is a foam block under the seat in the channel, but nothing under the cheeks. The other boats are similar to the Pyranha, in comparison to, say, Jackson Elite outfitting. Perhaps that is why foam under the rest of the seat would help, yes? Better weight distribution over a larger area?

I've had the same problem for the last year or more. My burn has a nice pregnancy under the seat. I've discovered there isn't much you can do other than keep paddling it, or sell it. I too have an affinity for rock boofs, slides, and splats, so one can only assume that the more you abuse it the more mucked up the hull will get.

The only Advice I can give is call it a "boof button" and not an oil can, it has less negative association, and makes you feel better about it when you feel that thing air you out off of a nice rock-slide-to-boof-stomp. Embrace the button and shun the can.

Hahaa! Nice, Jed. Would you echo other sentiments about increased crack potential, though?

Currently experimenting with balancing a boat on a piece of wood (with some other item at the bow to keep the boat level), in hopes the normal weight will coax a reduced protrusion. Probably won't do much, and I'll likely place it in the sun tomorrow at work.

I still feel there has to be something more than just a bit of rock grinding going on. The Pyranha has been in my possession for about a month, and six of the thirteen outings it has seen were on Wenatchee. Two Upper Greens, two Lower, and the rest MM, but none of them at really low water. I'm sure it is a factor, but I still feel there might be something abou how I press against the boat interior that is to blame. But why and how come his isn't seen more often is perplexing. I'm not a stellar boater, so not like I'm doing the latest crazy air maneuvers and tourquing about.

Makes me wonder, I just thought of something......got an experiment I might do......

In all my field research I've come to a couple of conclusions. Conclusion A) kayaking is tough on kayaks. conclusion B) some people break lots of kayaks, some don't. I've had a preggo boat for over a year and have gotten lot's of river miles, portages, throw and goes, and boofs out of that hull. It's still preggo, still not compromised. But that being said the logic points towards oil canning/boof buttons are more likely to crack/wear out. My field research has not reached a conclusion in regards to this hypothesis, but I think it's safe to say, mucked up boats are more likely to break that un-mucked up boats.

Final thought, call pyranha, ask them if they had any reports of bad batches. Maybe they'll send you some stickers.

A bit of the sun trick for the Pyranha, as well as very managed weighting on the bump (both with the hull up and a weight on top as well as a raised solid perch and a bit at whichever end to center the load with the hull down).

The WS is doing much better, but I addressed it a bit later in the formation. Now all that is left is a slight depression behind where the bump used to be.

Thanks for the advice guys!

And now a thought:
I had been getting lazy while surfing. Instead of lifting my knees I was leaning back. Confidence and a little fatigue has led me to slouching in evening sessions, too. Also makes my back ache when cartwheeling (vs a straighter back). This explains why it was taking me a bit to get my hips beneath me and surf like I know I can. I think this is the culprit. I slouch and lean back when lazy, instead of sitting up straight and lifting my knees to counter my bow diving more than I'd like. Like sheet metal, bent surfaces in plastic have more rigidity, and the flat surface in the center of a planing hull is an easy target placed perfectly to deflect. Managing my technique kept my hull flat this weekend and provided the fun on water I was looking for.

Just like rotating for a paddle stroke instead of "bicycling with the arms," technique is everything.....

Still haven't figured out timing on Blunts though. [kicks a rock w/hands in pockets while skulking]

I recently restored an old playboat that was badly oil-canned from inproper storage. To make things worse, it's a "comp" weight boat with a thinner layup. My goal was to restore the hull to a relatively flat shape so I could use the boat specifically for ocean surfing.

To accomplish my goal, I did three things:

(1) I removed all of the components except the bare hull...this included both pillars and the entire seat structure.

(2) I placed the boat in the sun for a few hours with the hull facing skyward. On previous boats, I tried boiling water, hair dryers and sunshine. The best of all of these by far (and the easiest) was sunshine.

(3) When I reassembled the boat, I ran two parallel 1/2" PVC pipes down along the inside of the seat plate that connects the front and rear pillars. These pipes are double-bolted (on each end) with stainless fasteners.

The main goals of this project were to reform the hull (heat) as best I could and then to strengthen the hull (PVC) to prevent any further deformities. The PVC technique was borrowed from a few C-1 boaters I seen who've used piping to strengthen the hull after removing the seat components. The great thing is that it's strong, relatively lightweight and it distributes any load (like that of the seat) across the length of the pipe.

The boat is a Dagger Super Ego. In this case, there's a flat plate (with lengthwise ridges) that runs underneath the front pillar, seat and rear pillar. There was enough area to run the pipes in between the ridges on top of the plate. These were then bolted with 1/16" fasteners (round end underneath the plate) and set in place with lock nuts on the top of the pipe. It's super strong and accounts for lengthwise stress.

So, musing about all this, and after seeing Jean-Luc's boats, I wonder.....

If the immediate doesn't do, what will the aftermarket?

Having problems with my backband from the manufacturer leads me to aftermarket options. The automotive industry has been doing it for years.

Could we potentially see hull stiffening upgrades? Foam core, woven fibre shell inserts designed to fit into known hulls and existing outfitting that provide rigidity at minimal weight, while not being outrageously expensive and having actual perceivable benefits.

Just musing on weight distribution on a hull from a given seating arrangement.

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